Of course, I am myself somewhat passionate about my own choices - but I see benefits in (almost) all FF systems, including one most people will discard out of hand, the M mount.
Here are a few thoughts on the benefits of some systems I can see:
- Sony (F)E mount: Vastly popular, lots of lens options, innovative bodies, many of which can be seen as pioniering key features and technical achievements that became benchmarks. The place to look for a kind of "leader" in the mirrorless field: Sony keeps pushing the envelope and forces everyone else to try and keep up.
- L mount: a joint effort (something we see all too rarely in the industry, the other, , being even more impressive, but not FF), very ambitious as well as very interesting lens options. With the arrival of the Panasonic S5 II, there's a superb entry point to the system available - and the older S5 isn't to be sneezed at either. Through the L mount Alliance, the way the lens system develops is quite impressive.
- Nikon Z (a word of warning: my choice!): great handling bodies with well-judged features (consistently good EVFs in all models, confidence-inspiring levels of sealing and sturdiness, effective I.B.I.S. in all models), judicious backward compatibility (including native adapters that allow you to make the best of former Nikon F lenses, especially ones with built-in AF motors), and last, but not least, a very well judged lens system that gets fleshed out in a very convincing manner - very well thought through, no major gaps, no curious multi-strategic approach, straightforward and resulting in great quality, well-priced (if not cheap, as a rule) offerings. At this point, I'll repeat the warning once more: I've put my money where my mouth is with this system because of its merits. YMMV, of course.
- Leica M mount: Many aspects of its technological foundations may appear outdated, but there's no other system you can get more interesting and optically fantastic lenses for; small and portable, but very expensive bodies, wonderful, but of course quirky shooting experience. You'll either love it or hate it. I love it - in fact, in spite of my infatuation with Nikon Z, I'd have a hard time deciding against my M mount gear if I was forced into only maintaining one system.
Please note that I will not comment on Canon RF because my take on it is somewhat critical, but mainly, I completely lack experience with it. Better informed people will doubtlessly chime in on that system.
There are, of course, also very well established DSLR mounts, like Pentax K, Canon EF and Nikon F. But my guess is that this thread wasn't meant to cover them as well. However, since it's possibly meant to show entry points, I will say here that I see great potential in many DSLRs for beginners and enthusiasts alike.
- While Pentax offers basically one model (with two iterations), the K-1 is a powerful beast of a camera and offers something unique in the FF DSLR world: I.B.I.S. It's big and heavy, but handling is great, and results are stunning, as the small, but very competent group of users on this forum have clearly shown. For me, it's the DSLR that's still competitive in today's expanding field of mirrorless FF options. Plus it works impressively well with the multitude of K mount lenses available.
- Canon EF offers the most inexpensive entry point to FF DSLRs, and their models were always considered benchmarks in their day. I have very limited experience with their cameras (I've been able to use a 5D II and a 5DSR for very short periods of time - and it's a long time since), but I found them very well thought through, and results were very impressive, though the 5DSR was kind of quirky and very difficult to get things right with due to its huge pixel count in a body that lacked any supportive technologies (like, most of all, I.B.I.S.). But the 6D and 6D II still are impressive bodies and can be hand quite cheap as well even though they're quite recent (at least the 6D II). In fact, if I ever decided to buy into a system just for the joy of playing with it, an early 5D or 5D II may well be my pick ...
- I still love my Nikon D750. Any model from the D600 to the D850 will be rewarding to shoot, very well made and reliable. There are a couple of caveats with certain D600 and D750 models - but you can check for affected batches online. Furthermore, the current D780 packs all the strengths of the D750 in an even more durable body and adds most of the desirable features of the Z 6, though with the notable exception of I.B.I.S. If you're into using LiveView on a DSLR, there's none better, though - which is kind of surprising, considering how well Canon's bodies handle that task as well. That said, my recommendation still goes to the D750 - for what you pay for it, you get a fantastic camera that's also pretty compact by DSLR standards, as well as - should you choose to set it up that way - very beginner-friendly. And don't forget that the F mount as a very long, very proud history.
Lastly, please take everything said above with a grain of salt. I may appear to be a Nikonite or Nikon fanboy, but note that I tried quite a few systems and
came back to Nikon. This includes, of all things, Sony FE. There are many reasons for me to prefer Nikon's offerings. However, familiarity may play a decisive part in my take, so please, don't see this as anything else but an opinion - if I said something, anything you find controversial, please tell me, and I'll either remove it or correct it.
M.
P.S. First and foremost, I tried to set a tone with this post; in truth, I'm not all that keen on propagating my own choices - because they're mine and based on my needs and preferences, yours may differ fundamentally. I just hope we can keep this thread trucking on in this kind of manner ...